The present invention relates generally to optical displays, and, more specifically, to a heads up display.
In a vehicle such as an automobile or aircraft, an operator sits behind an instrument panel and windshield for controlling operation of the vehicle. The instrument panel contains various instruments of interest in operating the vehicle, including a velocity indicator for example. In order to allow the operator or observer to maintain constant observation of the external environment beyond the windshield, it is desirable to provide a heads up display (HUD) which superimposes desired instrument information over external images transmitted through the windshield so that both may be viewed simultaneously.
In a typical application, a HUD panel is positioned between the observer and the windshield and must be transparent for allowing external images to be seen by the observer directly through the panel. The panel and the windshield are two separate entities since the HUD panel is a sophisticated device for projecting an image therein while at the same time allowing external images to be seen. A typical HUD panel is a flat glass plate with reflective and non-reflective coatings on opposite sides for allowing simple reflection of a cathode ray tube (CRT) image while allowing external viewing. In another example, optical gratings are used for diffracting internal light at an outlet aperture of a glass plate for viewing by the observer. Since diffraction is directional in this HUD panel, the observer's field of view is limited, and therefore requires an optimum position of observation for clearly viewing the display image.